Add namespacing for observer generator

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

activerecord/lib/rails/generators/active_record/observer/templates/observer.rb

+<% module_namespacing do -%>
 class <%= class_name %>Observer < ActiveRecord::Observer
 end
+<% end -%>

railties/lib/rails/generators/test_unit/observer/templates/unit_test.rb

 require 'test_helper'
 
+<% module_namespacing do -%>
 class <%= class_name %>ObserverTest < ActiveSupport::TestCase
   # Replace this with your real tests.
   test "the truth" do
     assert true
   end
 end
+<% end -%>

railties/test/generators/namespaced_generators_test.rb

 require 'generators/generators_test_helper'
 require 'rails/generators/rails/controller/controller_generator'
 require 'rails/generators/rails/model/model_generator'
+require 'rails/generators/rails/observer/observer_generator'
 
 class NamespacedGeneratorTestCase < Rails::Generators::TestCase
   def setup
@@ -128,3 +129,24 @@ def test_invokes_default_test_framework
     assert_file "test/fixtures/test_app/accounts.yml", /name: MyString/, /age: 1/
   end
 end
+
+class NamespacedObserverGeneratorTest < NamespacedGeneratorTestCase
+  include GeneratorsTestHelper
+  arguments %w(account)
+  tests Rails::Generators::ObserverGenerator
+
+  def test_invokes_default_orm
+    run_generator
+    assert_file "app/models/test_app/account_observer.rb", /module TestApp/, /  class AccountObserver < ActiveRecord::Observer/
+  end
+
+  def test_invokes_default_orm_with_class_path
+    run_generator ["admin/account"]
+    assert_file "app/models/test_app/admin/account_observer.rb", /module TestApp/, /  class Admin::AccountObserver < ActiveRecord::Observer/
+  end
+
+  def test_invokes_default_test_framework
+    run_generator
+    assert_file "test/unit/test_app/account_observer_test.rb", /module TestApp/, /  class AccountObserverTest < ActiveSupport::TestCase/
+  end
+end